It is well documented that atrial fibrillation (AF), either alone or as a consequence of other cardiac disease, continues to persist as the most common type of cardiac arrhythmia. In the United States, AF currently affects an estimated two million people, with approximately 160,000 new cases being diagnosed each year. The cost of treatment for AF alone is estimated to be in excess of $400 million worldwide each year.
Although pharmacological treatment is available for AF, the treatment is far from perfect. For example, certain antiarrhythmic drugs, like quinidine and procainamide, can reduce both the incidence and the duration of AF episodes. Yet, these drugs often fail to maintain sinus rhythm in the patient. Cardioactive drugs, like digitalis, Beta blockers, and calcium channel blockers, can also be given to control AF by restoring the heart's natural rhythm and limiting the natural clotting mechanism of the blood. However, antiarrhythmic drug therapy often becomes less effective over time. In addition, antiarrhythmic drug can have severe side effects, including pulmonary fibrosis and impaired liver function.
Another therapy for AF is surgery. In a technique known as the “Maze” procedure, a surgeon makes several incisions through the wall of the atrium with a scalpel and then sews the cuts back together, creating a scar pattern. The scars isolate and contain the chaotic electrical impulses to control and channel the electrical signals. The Maze procedure is expensive, complicated to perform, and associated with long hospital stays and high morbidity.
An alternative to open heart or open chest surgery is a minimally invasive treatment in which ablation devices are used to form scars in various locations in the atrial tissue. Ablation devices that apply heat or cold to body tissue are known. Typically, these devices have an elongate, highly-flexible shaft with a steerable distal end for negotiating a path through the body of a patient. Rigid shaft devices are used in more invasive procedures where a more local opening or direct access to a treatment site is available or created.
It is important to note that these devices are used in an attempt to ablate tissue through the full thickness of the cardiac wall, and thus create a risk associated with damaging structures within or on the outer surface of the cardiac wall. Accordingly ablation devices have been developed which include opposing jaw members to ablate tissue from both sides of the cardiac wall. For example, U.S. Pat. No. 6,161,543 to Cox; U.S. Pat. No. 5,733,280 to Avitall; and U.S. Pat. No. 6,517,536 to Hooven describe techniques for ablating tissue of organs or vessels having opposing walls and disclose ablation devices having clamping members to clamp a treatment site therebetween. Such devices include rigid members/shafts to facilitate reaching the tissue treatment site.
While rigid shafts may be useful in some applications, they have certain limitations as well. For example, without a preset shape for reaching a particular location in the body of a patient, the rigid nature of the shaft limits the area of tissue that can be reached and treated. Even where a relatively large incision is provided, tissue areas that are not at least somewhat directly accessible cannot be reached.
Although a rigid shaft can be provided with a predetermined shape, one must select a device with a rigid shaft that has the most appropriate shape for positioning the working portion of the device in contact with the treatment site in view of the particular anatomical pathway to be followed in the patient. It will be appreciated that a large inventory of devices having rigid shafts may be required to accommodate the various treatment sites and patient anatomies. As an example, U.S. Pat. No. 6,161,543 to Cox el al. describes a variety of rigid probe shapes. Further, for a patient having a relatively uncommon anatomic configuration and/or a difficult to reach treatment site, all rigid devices of an existing set may have less than optimal shapes for positioning. This may impair the prospects of successfully carrying out the treatment procedure. For an ablation device which must bear against tissue at the remote region to create lesions, the contour followed by the device in reaching the target site will in general further restrict the direction and magnitude of the movement and forces which may be applied or exerted on the working portion of the device to effect tissue contact and treatment.